Method and apparatus for improving integrity of processor voltage supply with support for DVFS

ABSTRACT

Dedicated circuitry may monitor a processor supply voltage and provide additional power on a temporary nano-second scale basis to the processor when the supply voltage drops below predetermined levels. This may be done without explicit knowledge of a commanded supply voltage level for the processor.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 62/635,322, filed on Feb. 26, 2018,the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Aspects of the invention relate to voltage regulation for semiconductordevices, and more particularly to mitigating voltage droops in aregulated voltage supply for semiconductor devices.

Reliable continuous operation of a high-performance processor, forexample a CPU or GPU (processor) often depends on integrity of a voltagesupply to its processing circuitry. For example, during sudden onset ofa processor's operational activity (which may be referred to as loadstep transient, load step event, or transient event), the supply voltagemay temporarily droop. Often a transient-related voltage margin may beutilized in a power supply design to account for transient voltagedroops, to attempt to ensure reliable continuous operation of theprocessor at its chosen operating frequency.

An active transient control block may be used to reduce voltage droops.An active transient control block generally includes circuitry forproviding additional power to a load on the occurrence of a negativetransient change in supplied voltage. Use of an active transient controlblock may relax transient-related voltage margin requirements, thuseffectively providing a useful voltage credit which can be used toincrease a processor's operating frequency, and/or reduce a processor'spower consumption, and/or increase manufacturing yield at higheroperating frequency, and/or reduce Processor's silicon area. PUBLISHEDPAPER: H. Mair, et al., “A 10 nm FinFET 2.8 GHz Tri-Gear Deca-Core CPUComplex with Optimized Power-Delivery Network for Mobile SoCPerformance”, ISSCC, p. 56-57, 2017, the disclosure of which isincorporated by reference herein.

However, processors may be configured to operate at different voltagelevels. In some cases the voltage levels may be set statically, forexample depending on a system in which the processor is configured tooperate. In some cases the voltage levels instead or in addition may bedynamically changed during operation, for example due to dynamic voltageand frequency scaling (DVFS) operations. In either case, circuitrypreconfigured to account for transient voltage droops may havedifficulties in being able to properly respond in the case of differingdesired voltage level of the processor.

BRIEF SUMMARY OF THE INVENTION

Some embodiments provide an apparatus and/or method for mitigation ofsupply voltage droops. Some embodiments provide for automatic transientcontrol responses without predetermined knowledge of a processor'svoltage target. In some embodiments an active transient control block isagnostic to a processor's voltage target. In some embodiments the activetransient control block is independent of DVFS implementations and/orcommands. In some embodiments the active transient control block isagnostic to DVFS implementations and/or commands. Some embodimentsprovide voltage droop responses with sub-nanosecond response times.

Some embodiments provide circuitry for compensating for voltage droop inpower supplied to a load, comprising: a first low pass filter with afirst time constant configured to filter a signal indicative of voltageprovided to the load to provide a first low pass filtered signal; asecond low pass filter with a second time constant configured to filterthe signal indicative of voltage provided to the load to provide asecond low pass filtered signal, the second time constant less than thefirst time constant; an offset generator configured to generate at leastone voltage level that is a percentage of the first low pass filteredsignal indicative of voltage provided to the load; a first sensorconfigured to determine that the second low pass filtered signal is lessthan the at least one voltage level; and control circuitry configured toactivate at least one switch coupling a higher voltage source supply tothe load in response to the first sensor determining that the second lowpass filtered signal is less than the at least one voltage level.

Some embodiments provide a method of compensating for voltage droop inpower supplied to a load, comprising: determining that a signalindicative of voltage supplied to the load, to provide power to theload, is less than at least one predetermined percentage of a delayedversion of the signal indicative of voltage supplied to the load; inresponse to determining that the signal indicative of voltage suppliedto the load is less than the at least one predetermined percentage ofthe delayed version of the signal indicative of voltage supplied to theload, coupling a higher voltage source supply to a higher level voltagerail providing power to the load.

These and other aspects of the invention are more fully comprehendedupon review of this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of a voltage regulation system for a loadincluding an active transient control (ATC) block in accordance withaspects of the invention.

FIG. 2 is a block diagram of an embodiment of an ATC block coupled to aload, in accordance with aspects of the invention.

FIG. 3 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention, with thefurther embodiment showing an example of low pass filters and thevoltage sensor array of the ATC block of FIG. 2.

FIG. 4 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention, with thefurther embodiment showing a further example of the voltage sensor arrayof the ATC block of FIG. 2.

FIG. 5 is a semi-schematic semi-block diagram of example low-passfilters, droop offset generator, and single voltage sensor for an ATCblock, in accordance with aspects of the invention.

FIG. 6 is a semi-schematic semi-block diagram of a further examplelow-pass filters, droop offset generator, and voltage sensor array foran ATC block, in accordance with aspects of the invention.

FIG. 7 is a semi-schematic semi-block diagram of a yet further examplelow-pass filters, droop offset generator, and voltage sensor array foran ATC block, in accordance with aspects of the invention.

FIG. 8 is a schematic illustrating example low pass filters for use inan ATC block in accordance with aspects of the invention.

FIG. 9 is a table indicating example output settings for droop sensorsin accordance with aspects of the invention.

FIG. 10 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention.

FIG. 11 is a semi-schematic semi-block diagram of an example low-passfilters, droop offset generator with current bias, and a single voltagesensor for an ATC block, in accordance with aspects of the invention.

FIG. 12 is a semi-schematic semi-block diagram of a further examplelow-pass filters, droop offset generator with current bias, and avoltage sensor array for an ATC block, in accordance with aspects of theinvention.

FIG. 13 is a semi-schematic semi-block diagram of a yet further examplelow-pass filters, droop offset generator with current bias, and avoltage sensor array for an ATC block, in accordance with aspects of theinvention.

FIG. 14A-C illustrate embodiments of voltage sensors in accordance withaspects of the invention.

FIG. 15 is a graph of activation of power switches and voltage drooperror, in accordance with aspects of the invention.

FIG. 16 is a further example graph of activation and deactivation ofpower switches in time upon a single full-magnitude droop event, inaccordance with aspects of the invention.

FIG. 17 is a further example graph of activation and ramped-downdeactivation feature of power switches in time upon a singlefull-magnitude droop event, in accordance with aspects of the invention.

FIG. 18 is a further example graph of activation and ramped-downdeactivation feature of power switches with a per-thresholdauto-limiting feature in time upon a single full-magnitude droop event,in accordance with aspects of the invention.

FIG. 19 is a further example graph of activation and ramped-downdeactivation feature of power switches with a global auto-limitingfeature in time upon a single full-magnitude droop event, in accordancewith aspects of the invention.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a voltage regulation system for a loadincluding an active transient control (ATC) block in accordance withaspects of the invention. In the embodiment of FIG. 1, a voltageregulator 111 provides power to a processor load 113. In mostembodiments the load comprises semiconductor circuitry, and may be forexample a processor, processor core, CPU cluster or other semiconductorlogic circuitry. The voltage regulator may be, for example, a DC-DCswitching converter, and the voltage regulator may be in a buckconfiguration, a boost configuration, a buck-boost configuration, orsome other configuration. In some embodiments the semiconductorcircuitry is that of a handheld device, for example a smartphone, withthe voltage regulator regulating power provided by a battery. Toconserve battery power, and for other reasons, in various embodiments adesired voltage level for the load may vary dynamically, for example asdetermined and commanded from time-to-time by a dynamic voltage andfrequency scaling block (not shown).

Power drawn by the load may also vary substantially over time, dependingon activity of the processor(s) making up the load. Moreover, the powerdrawn by the load may increase very quickly, over very few clock cycles.In such instances, the voltage provided to the load by the voltageregulator may suddenly drop, or exhibit a voltage droop, that may resultin improper operation of the load.

Accordingly, the system of FIG. 1 includes an ATC block 115. The ATCblock is coupled to a power source 117. The ATC block monitors foroccurrence of a voltage droop, and provides additional power from thepower source to the load in the detected event of a voltage droop.Moreover, the ATC block of FIG. 1 does so without being provided asignal indicative of a commanded voltage level for power supplied to theload. As illustrated in FIG. 1, the ATC block provides the additionalpower to the load in parallel to the power provided to the load by thevoltage regulator.

FIG. 2 is a block diagram of an embodiment of an ATC block 115 coupledto a load, in accordance with aspects of the invention. The ATC blockreceives sense signals indicating voltage of power rails of the load,with the load being shown as a CPU cluster. In some embodiments, and asillustrated in FIG. 2, the power rails include a lower level voltagerail at ground, and a higher level voltage rail above ground. As onewould understand, in various implementations the lower level voltagerail may not be at ground, with the lower level voltage rail beingsimply at some voltage lower than the higher level voltage rail. In someembodiments the ATC block is coupled directly to the power rails, insome embodiments the ATC block receives signals at a voltage equal tothe voltage levels of the rails, or a scaled version of the voltagelevels of the rails.

Low-pass filters 227 of the ATC block receive the sense signalsindicating voltage levels of the rails. The low-pass filters providevoltage signals to a droop offset generator 229 and a voltage sensorarray 223. In various embodiments the low-pass filters serve to providea delay, programmable in some embodiments, to the voltage signalsprovided to the droop offset generator and the voltage sensor array. Insome embodiments the voltage signal to the droop offset generator isdelayed by an amount greater than the voltage signal to the voltagesensor array. In some embodiments only one low-pass filter is used, forthe signal to be provided to the droop offset generator.

The droop offset generator generates one or more voltage levels believedto be indicative of a droop detection thresholds. The droop offsetgenerator generates the voltage levels based on the voltage signalprovided by the low-pass filters. In some embodiments the one or morevoltage levels believed to be indicative of droop detection thresholdsare fixed percentages of the voltage signal provided by the low-passfilters. In some embodiments the one or more voltage levels believed tobe indicative of droop detection thresholds are programmable percentagesof the voltage signal provided by the low pass filters.

The voltage sensor array compares the voltage signal from the low-passfilters with the one or more voltage levels believed to be indicative ofdroop detection thresholds. As indicated above, in some embodiments thevoltage signal provided to the droop offset generator is delayed for agreater amount of time than the voltage signal provided to the voltagesensor array. Accordingly, even though the low-pass filters providesignals to both the droop offset generator and the voltage sensor array,in such embodiments a drop in voltage of power supplied to the CPUcluster will be exhibited as a drop in voltage in the voltage signalprovided to the voltage sensor array prior to a corresponding decreasein output of the droop offset generator. The voltage sensor array,therefore, determines if voltage supplied to the load exhibits a drop involtage below the voltage levels believed to be indicative of voltagedroop.

Results of the comparisons performed by the voltage sensor array areprovided to a digital activation control block 225. The digitalactivation control block creates an activation code based on the resultsof the comparisons performed by the voltage sensor array. In someembodiments the activation code is provided by the digital activationcontrol block on a plurality of signal paths, for example with one bitof the activation code provided on each of the plurality of signalpaths.

A power switch array 221 receives the digital activation code. Based onthe digital activation code the power switch array activates none, oneor a plurality of switches to provide power from a higher voltage sourcesupply 217 to the CPU cluster, for example by coupling the highervoltage source supply to the higher level voltage rail by way of theactivated switches. In some embodiments the power switch array includesa plurality of switches in parallel coupling the higher voltage sourcesupply to the CPU cluster. In some embodiments different ones of thepaths are configured to provide different amount of power to the CPUcluster. In some embodiments each of the paths are configured to providethe same amount of power to the CPU cluster. In some embodiments thepower switch array is as discussed in U.S. Pat. No. 9,515,553, thedisclosure of which is incorporated herein in its entirety. In someembodiments the power switches are implemented in banks of powerswitches, and the different banks of power switches may be located indifferent areas of a semiconductor. For example, in some embodiments onebank of power switches may be located on one side of circuitry for thedroop offset generator, voltage sensors, and digital control, and onebank of power switches may be located on an opposing side of thecircuitry for the droop offset generator, voltage sensors, and digitalcontrol. In some embodiments each of the power switches share a sametrimming code.

FIG. 3 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention, with thefurther embodiment showing an example of low-pass filters and thevoltage sensor array of the ATC block of FIG. 2. The embodiment of FIG.3, like the embodiment of FIG. 2, shows a CPU cluster 213 with a powerrail coupled to an ATC block 115. A power switch array 221 of the ATCblock couples a voltage supply source 217 to the power rail of the CPUcluster.

The ATC block of the embodiment of FIG. 3 includes an offset low-passfilter 331, an input low-pass filter 333, and a zero crossing low-passfilter 335. The offset low-pass filter provides a filtered voltagesignal Vofs to a droop offset generator 329, with the droop offsetgenerator generating an alarm threshold signal Valarm and a droopthreshold signal Vdrp. In some embodiments the Valarm signal is set to avoltage greater than the voltage of the Vdrp signal. In someembodiments, however, the Valarm signal is set to a voltage less thanthe voltage of the Vdrp signal. The input low-pass filter provides afiltered voltage signal Vin, which is compared to the Valarm and Vdrpthreshold signals by voltage sensors 323. The zero crossing low-passfilter provides a zero crossing threshold signal Vzc, which is comparedto the filtered signal Vin by voltage sensors 323.

In some embodiments the low-pass filters are implemented using RCcircuits. In some embodiments the low-pass filters have programmabletime constants. In some embodiments the time constant of the inputlow-pass filter is less than the time constants of the offset low-passfilter and/or the zero crossing low-pass filter. In some embodiments thetime constant of the input low-pass filter is between 0-0.5 nanoseconds.In some embodiments the time constant of the zero crossing low-passfilter is between 0.5-5 nanoseconds. In some embodiments the timeconstant of the offset low-pass filter is between 10-100 nanoseconds. Inone embodiment the time constant of the input low-pass filter is 0.2nanoseconds, the time constant of the zero crossing low-pass filter is 2nanoseconds, and the time constant of the offset low-pass filter is 20nanoseconds.

Results of the comparisons by the voltage sensors are provided to adigital control 325. The digital control sets an activation codecommanding a number of switches of the power switch array to activate.In some embodiments the digital control sets the activation code toincrease the number of active power switches, up to all of the powerswitches, for each clock cycle, or each of a number of programmableclock cycles, for a voltage droop situation, in which the voltagesensors indicate that the Vin signal is less than the Vdrp signal. Insome embodiments the digital control sets the activation code todecrease the number of active power switches, up to all of the powerswitches, for each clock cycle, or each of a number of programmableclock cycles, for a no voltage droop situation in which the voltagesensors indicate that the Vin signal is not less than the Vdrp signal.In some embodiments the digital control also considers that a no voltagedroop situation exists, regardless of whether the voltage sensorsindicate a voltage droop situation, if the voltage sensors indicate thatVin is greater than Vzc, which would indirectly indicate that Vin isincreasing. In some embodiments, for example embodiments in which Valarmis set higher than Vdrp, the digital control deactivates all of thepower switches if the voltage sensors indicate an alarm condition, withVin greater than Valarm. In some embodiments, however, for exampleembodiments in which Valarm is set lower than Vdrp, the digital controlmay provide a platform notification whenever Vin is less than Valarm. Insome embodiments the platform notification may be in the form of adedicated signal provided to a platform hosting the CPU cluster (or asystem-on-chip SOC processor of the platform). In some embodiments theplatform notification may be in the form of an interrupt signal to theplatform.

In some embodiments, and as illustrated in FIG. 3, the digital controlsets a digital offset control signal, used by the droop offset generatorin setting the droop threshold signal Vdrp. In some embodiments thedigital control sets the digital offset control signal to command use ofa higher value for Vdrp, up to a predefined maximum value, for eachcycle a droop situation exists. In some embodiments, the digital controloffset signal is reset to command use of a minimum value for Vdrp, orsimply a lower value, when the droop situation no longer exists.

FIG. 4 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention, with thefurther embodiment showing a further example of the voltage sensor arrayof the ATC block of FIG. 2. The embodiment of FIG. 4 is similar to theembodiment of FIG. 3, with the embodiment of FIG. 4 including aplurality of voltage droop indications. The use of a greater number ofdroop indicators may provide for increased flexibility in responding tovoltage droop situations, although the use of additional numbers ofvoltage sensors to do so may result in an increase in area of and powerusage by the voltage sensors.

The embodiment of FIG. 4, like the embodiment of FIG. 2, shows a CPUcluster 213 with a power rail coupled to an ATC block. A power switcharray 221 of the ATC block couples a voltage supply source 217 to thepower rail of the CPU cluster. Like the embodiment of FIG. 3, embodimentof FIG. 4 includes an offset low-pass filter 331, an input low-passfilter 333, and a zero crossing low-pass filter 335, for example asdiscussed with respect to FIG. 3.

A droop offset generator 429 of FIG. 4, however, generates a pluralityof droop threshold signals Vdrp0,Vdrp1 Vdrpn, in addition to a Valarmsignal. Each of the plurality of droop threshold signals are atdifferent voltage levels, with for example Vdrp0 being a higher voltagethan Vdrp1, which is higher than Vdrp2, etc. Similarly, the voltagesensors compare Vin, from the input low-pass filter, with each of thedroop signals, in addition to performing the Valarm and Vzc comparisonsas discussed with respect to FIG. 3.

A digital control 425 sets an activation code for activating switches ofthe power switch array. In some embodiments the digital control sets theactivation code based on the number of voltage sensors indicating adroop condition. In some embodiments the digital control sets theactivation code as discussed with respect to the embodiment of FIG. 3and additionally the number of voltage sensors indicating a droopcondition. For example, in some embodiments the digital control sets theactivation code to activate a percentage of power switches based on apercentage of voltage sensors indicating a droop condition.

FIG. 5 is a semi-schematic semi-block diagram of example low-passfilters, droop offset generator, and single voltage sensor for an ATCblock, in accordance with aspects of the invention. In FIG. 5 an offsetlow-pass filter 331 and an input low pass filter 333 are shown, althoughit is noted that some embodiments additionally include a zero crossinglow-pass filter. Each of the offset low-pass filter and the input lowpass filter are shown as RC circuits. An input to the RC circuit iscoupled to a CPU high power rail (or signal line indicative of voltageof the CPU high power rail) and the capacitor of the RC circuit iscoupled to the CPU low power rail (or signal line indicative of voltageof the CPU low power rail), which might be ground (and is discussed asground generally herein).

The output of the offset low-pass filter is provided as an input to adroop offset generator 529. The droop offset generator couples thisinput to a voltage divider 531, illustrated as a series of resistorscoupled to ground. For illustrative purposes, the droop offset generatorof FIG. 5 only outputs one Vdrp signal. The Vdrp signal is a voltagefrom the voltage divider selected by a multiplexer 533, with theselected voltage provided as a Vdrp signal to a voltage sensor 535 forcomparison with the output of the input low pass filter. In theembodiment of FIG. 5, the voltage selected is dynamically selected asdetermined, for example, by a digital control, for example the digitalcontrol of FIGS. 2-4. The digital control may determine the selectionbased on, for example, a frequency of occurrence of voltage droops, anindication of a minimum voltage for which a CPU of a CPU cluster hasbeen designed to operate without logic errors, or other factors. In someembodiments, and as illustrated in FIG. 3, the digital control sets adigital offset control signal, used by the droop offset generator inselecting the voltage provided as the Vdrp signal. In some embodimentsthe digital control sets the digital offset control signal to commanduse of a higher value for Vdrp, up to a predefined maximum value, foreach cycle a droop situation exists. In some embodiments, the digitalcontrol offset signal is reset to command use of a minimum value forVdrp, or simply a lower value, when the droop situation no longerexists.

FIG. 6 is a semi-schematic semi-block diagram of a further examplelow-pass filters, droop offset generator, and voltage sensor array foran ATC block, in accordance with aspects of the invention. Theembodiment of FIG. 6 is similar to that of FIG. 5, with the offsetlow-pass filter 331, the input low-pass filter 333, and a droop offsetgenerator 529. The droop offset generator 529 of the embodiment of FIG.6, however, provides a plurality of voltage droop voltage levels, andcorrespondingly includes a plurality of voltage sensors 635 forcomparing voltage droop voltage levels with an output of the inputlow-pass filter. In addition, the multiplexer of the embodiment of FIG.6 is shown as being statically controlled.

FIG. 7 is a semi-schematic semi-block diagram of a yet further examplelow-pass filters, droop offset generator, and voltage sensor array foran ATC block, in accordance with aspects of the invention. Theembodiment of FIG. 7 is the same as that of the embodiment of FIG. 6,other than the multiplexers of the droop offset generator being providedboth dynamically and statically controlled. In some embodiments one ofthe droop signals is statically controlled, while others of the droopsignals are dynamically controlled.

FIG. 8 is a schematic illustrating example low-pass filters for use inan ATC block in accordance with aspects of the invention. The embodimentof FIG. 8 shows an offset low-pass filter 831, a zero crossing low-passfilter 835, and an input low-pass filter 833. Each of the filters areimplemented as RC circuits, with a variable resistance. In theembodiments illustrated in FIG. 8, a time constant of the offsetlow-pass filter may be varied between 10 and 100 nS, a time constant ofthe zero crossing low-pass filter may be varied between 0.5 and 5 nS,and a time constant of the input low-pass filter may be varied between 0and 0.5 nS. Accordingly, an output of the offset low-pass filter willalways be effectively delayed compared to an output of the inputlow-pass filter, and an output of the zero crossing low-pass filter willgenerally also be delayed compared to the output of the input low-passfilter, although the delay will be less than that provided by the offsetlow-pass filter.

FIG. 9 is a table indicating example output settings for droop sensorsin accordance with aspects of the invention. In some embodiments. Asindicated in the table of FIG. 9, droop sensors may indicate a tripcondition based on comparisons of Vin, which may be the output of theinput low-pass filter if present or an indication of voltage supplied tothe CPU cluster if not present, with different droop threshold levels.In general, a trip, or activate condition, is indicated if Vin dropsbelow the corresponding ones of the droop voltages provided to thevoltage sensors. In addition, the table of FIG. 9 indicates that thetrip conditions should be ignored or overridden if a comparison of Vinwith the output of the zero crossing low-pass filter indicates that Vinis increasing. In various embodiments the ATC blocks discussed hereinmay utilize the table of FIG. 9 in determining operations of theirdigital control blocks.

FIG. 10 is a block diagram of a further embodiment of an ATC blockcoupled to a load, in accordance with aspects of the invention. Theembodiment of FIG. 10 is similar to the embodiment of FIGS. 3 and 4,with the embodiment of FIG. 5 having a droop offset generator 1029 thatprovides only two voltage droop levels and corresponding changes to thevoltage sensor array 1023.

In the embodiment of FIG. 10 the droop offset generator dynamicallyvaries a first of the voltage droop levels, with a second of the voltagedroop levels remaining statically fixed. In some embodiments the firstof the voltage droop threshold levels is adjusted upward, for example ina step-wise fashion up to a predefined maximum, based on a signal fromthe digital control 1025 each cycle a voltage trip condition isindicated. Conversely, each cycle a voltage trip condition is notindicated, the signal from the digital control commands the voltagedroop threshold level to be decreased, for example in a step-wisefashion down to a predefined minimum. In many embodiments the predefinedminimum is above a voltage level set for the second of the voltage droopthreshold levels.

FIG. 11 is a semi-schematic semi-block diagram of an example low-passfilters, droop offset generator with current bias, and a single voltagesensor for an ATC block, in accordance with aspects of the invention.The embodiment of FIG. 11 is the same as that of FIG. 5, except thedroop offset generator 1129 of the embodiment of FIG. 11 utilizes acurrent mirror 1151 to provide a bias current for the voltage divider1131, which it is noted may be implemented with either transistors orresistors for the resistances of the voltage divider.

Similarly, FIG. 12 is also semi-schematic semi-block diagram of afurther example low-pass filters, droop offset generator with currentbias, and a voltage sensor array for an ATC block, in accordance withaspects of the invention. The embodiment of FIG. 12 corresponds to thatof FIG. 6, with the droop offset generator 1229 of FIG. 12 making use ofthe current mirror discussed with respect to FIG. 11.

For completeness, FIG. 13 is also presented. FIG. 13 is a semi-schematicsemi-block diagram of a yet further example low-pass filters, droopoffset generator with current bias, and a voltage sensor array for anATC block, in accordance with aspects of the invention. The embodimentof FIG. 13 corresponds to that of FIG. 7. As with the embodiment of FIG.12, the droop offset generator 1329 of FIG. 13 makes use of the currentmirror discussed with respect to FIG. 11.

FIGS. 14A-C illustrate embodiments of voltage sensors in accordance withaspects of the invention. The embodiment of FIG. 14A includes a clockedcomparator that outputs a result of a comparison of two inputs on aclocked basis. The embodiment of FIG. 14B includes two clockedcomparators that outputs a result of a comparison of two inputs on aclocked basis, with the two comparators clocked using out of phase clocksignals. Outputs of the two comparators are merged to provide a resultof the comparisons. In some embodiments the merging operation is an ORoperation, in some embodiments an AND operation, and in some embodimentsan exclusive OR operation. More than two comparators may instead beused. For example, the embodiment of FIG. 14C includes n comparators, ngreater than 2, with each of the n comparators clocked from differentphases of a clock signal. The different phases of the clock signal maybe provided, for example, by a multiphase PLL or DLL.

FIG. 15 is a graph of activation of power switches upon detection ofvoltage droop error, in accordance with aspects of the invention. Theactivation of power switches as indicated by FIG. 15 may be performed bythe ATC blocks discussed herein. In FIG. 15, additional power switchesare activated as a threshold is reached for each voltage droop level. Insome embodiments a different activation code is provided for eachvoltage droop level, and the activation code may have a one-to-onecorrespondence with a number of power switches to be activated. Forexample, in some embodiments there may be three voltage droop levels,three corresponding activation codes, with each activation codeactivating different numbers of power switches. In some such embodimentsthe number of power switches activated may be a percentage of the powerswitches corresponding to the percentage of voltage droop levels forwhich the threshold has been exceeded.

FIG. 16 is a further graph of activation and deactivation of powerswitches upon detection of a voltage droop event, in accordance withaspects of the invention. The activation and deactivation of powerswitches as indicated by FIG. 16 may be performed by the ATC blocksdiscussed herein. The graph of FIG. 16 is similar to that of FIG. 15,but additionally shows reducing the activation code (and hence thenumber of power switches activated) as Vin increases and trip signalsfor voltage droop levels are deactivated. In FIG. 16, as each tripsignal is deactivated, the activation code is decreased in a manneropposite to that of increase of the activation code, as discussed withrespect to FIG. 15.

FIG. 17 is a further graph of activation and ramped-down deactivationfeature of power switches upon detection of a voltage droop event, inaccordance with aspects of the invention. In some embodiments it may bedesirable to reduce a rate at which the power switches are deactivated,and FIG. 17 illustrates an example method of doing so. For FIG. 17, aplurality of power switches are associated with each increase ordecrease in the activation code (or alternatively, the power switcheseach have a plurality of different possible states for passing differentamounts of power). In FIG. 17, upon a reduction in the activation code,power switches are deactivated over time in a ramping manner, asillustrated by a solid line 1711, instead of deactivating all of thepower switches for an activation code all at once, as illustrated by adashed line 1713. As illustrated in FIG. 17, after a reduction of twolevels of the activation code, the activation code is held for a periodof time before the continuing reduction of the activation code for aslong as a voltage droop event notification, is active for example insome embodiments a DRP0 signal (in the context of FIG. 4).

FIG. 18 is a further graph of activation and ramped-down deactivationfeature of power switches with a per-threshold auto-limiting featureupon a voltage droop event, in accordance with aspects of the invention.In some embodiments it may be desirable to limit a maximum consecutivetime that power switches may be activated, or a maximum consecutive timethat a predetermined number of power switches may be activated, or amaximum consecutive time that a particular number of power switches maybe activated. In some embodiments the maximum time may be softwareconfigurable, and this may be done on a per level basis in someembodiments. In the example of FIG. 18, a maximum consecutive time thatpower switches may be activated is limited, and ramping down ofactivation of power switches begins at that time, regardless of thestate of the comparisons with the voltage droop levels. FIG. 18 showsthe ramping down 1811 of the switches based on the maximum consecutivetime period being reached, along with the ramping down that would haveotherwise occurred 1813 using the example of FIG. 17.

FIG. 19 is a further graph of activation and ramped-down deactivationfeature of power switches with a global auto-limiting feature upon avoltage droop event, in accordance with aspects of the invention. Insome embodiments in which the per-threshold auto-limiting feature isutilized, it may be beneficial to retain some power switches in anactive state, even if the maximum consecutive time limit has beenreached, so long as one voltage droop level trip signal remains active.FIG. 19 indicates this (with a first line 1911), with a ramping down ofactivation of power switches stopped at what FIG. 19 terms a GlobalLimit Activation Code, and a ramping down without such a feature shownfor comparison purposes (with a second line 1913).

Although the invention has been discussed with respect to variousembodiments, it should be recognized that the invention comprises thenovel and non-obvious claims supported by this disclosure.

What is claimed is:
 1. Circuitry for compensating for voltage droop inpower supplied to a load, comprising: a first low pass filter with afirst time constant configured to filter a signal indicative of voltageprovided to the load to provide a first low pass filtered signal; asecond low pass filter with a second time constant configured to filterthe signal indicative of voltage provided to the load to provide asecond low pass filtered signal, the second time constant less than thefirst time constant; an offset generator configured to generate at leastone voltage level that is a percentage of the first low pass filteredsignal indicative of voltage provided to the load; a first sensorconfigured to determine that the second low pass filtered signal is lessthan the at least one voltage level; and control circuitry configured toactivate at least one switch coupling a higher voltage source supply tothe load in response to the first sensor determining that the second lowpass filtered signal is less than the at least one voltage level.
 2. Thecircuitry of claim 1, further comprising a third low pass filter with athird time constant, the third time constant less than the first timeconstant and greater than the second time constant, the third low passfilter configured to filter the signal indicative of voltage provided tothe load to provide a third low pass filtered signal; and a secondsensor configured to determine that the second low pass filtered signalis greater than the third low pass filtered signal; wherein the controlcircuitry is further configured to disable activation of the at leastone switch coupling a higher voltage source supply to the load inresponse to the second low pass filtered signal being greater than thethird low pass filtered signal.
 3. The circuitry of claim 2, wherein thefirst time constant is 100 times the second time constant, and the thirdtime constant is 10 times the second time constant.
 4. The circuitry ofclaim 2, wherein each of the first low pass filter, second low passfilter, and third low pass filter include a variable resistance.
 5. Thecircuitry of claim 1, wherein the offset generator is configured togenerate additional voltage levels, each a different percentage of thefirst low pass filtered signal indicative of voltage provided to theload; and further comprising additional sensors, each configured todetermine that the second low pass filtered signal is less than acorresponding one of the additional voltage levels; and wherein the atleast one switch coupling the higher voltage source supply to the loadcomprises a plurality of switches; and wherein the control circuitry isconfigured to activate a number of the switches based on a number of thefirst sensor and additional sensors determining that the second low passfiltered signal is less than the at least one voltage level or theadditional voltage levels.
 6. The circuitry of claim 5, wherein thecontrol circuitry is configured to disable the switches in a rampingmanner over time.
 7. The circuitry of claim 5, wherein the controlcircuitry is configured to activate at least some of the switches for atmost a predetermined maximum consecutive time.
 8. A method ofcompensating for voltage droop in power supplied to a load, comprising:determining that a signal indicative of voltage supplied to the load, toprovide power to the load, is less than at least one predeterminedpercentage of a delayed version of the signal indicative of voltagesupplied to the load; in response to determining that the signalindicative of voltage supplied to the load is less than the at least onepredetermined percentage of the delayed version of the signal indicativeof voltage supplied to the load, coupling a higher voltage source supplyto a higher level voltage rail providing power to the load.
 9. Themethod of claim 8, wherein the at least one predetermined percentage isa fixed percentage.
 10. The method of claim 8, wherein the at least onepredetermined percentage is a programmable percentage.
 11. The method ofclaim 8, wherein the delayed version of the signal indicative of voltagesupplied to the load comprises the signal indicative of voltage suppliedto the load passed through a low pass filter.
 12. The method of claim 8,wherein the signal indicative of voltage supplied to the load comprisesa first signal from the higher level voltage rail passed through a firstlow pass filter, and the delayed version of the signal indicative ofvoltage supplied to the load comprises a second signal from the higherlevel voltage rail passed through a second low pass filter, and a timeconstant of the first low pass filter is less than a time constant ofthe second low pass filter.
 13. The method of claim 8, wherein the atleast one predetermined percentage of the delayed version of the signalindicative of voltage supplied to the load comprises a plurality ofpredetermined percentages, and wherein an extent of coupling of thehigher voltage source supply to the higher level voltage rail is basedon a number of instances for which the for which the signal indicativeof voltage supplied to the load is less than various ones of thepredetermined percentages of the delayed version of the signalindicative of voltage supplied to the load.
 14. The method of claim 13,further comprising generating an activation code based on the number ofinstances for which the signal indicative of voltage supplied to theload is less than various ones of the predetermined percentages of thedelayed version of the signal indicative of voltage supplied to theload, and wherein the activation code is used in activating switchescoupling the higher voltage source supply to the higher level voltagerail.
 15. The method of claim 14, further comprising determining thatthe signal indicative of voltage supplied to the load is greater than afurther delayed version of the signal indicative of voltage supplied tothe load, the further delayed version of the signal indicative ofvoltage supplied to the load being delayed less than the delayed versionof the signal indicative of voltage supplied to the load, and,responsive thereto, disabling coupling of the higher voltage sourcesupply to the higher level voltage rail.
 16. The method of claim 14,wherein the activation code is also used in deactivating the switchescoupling the higher voltage source supply to the higher level voltagerail.
 17. The method of claim 16, wherein the switches are deactivatedover time in a ramping manner.
 18. The method of claim 17, wherein atleast some of the switches are only activated for a predeterminedmaximum consecutive time.